Store your Music in Google Music (technically US only but there are ways and means...) and I guess other alternatives. Have access to all your music and stream it to your phone. Know your going to be offline? Know you want to listen to some specific albums? Download those to your device for offline play!
Photo's and Videos! Dropbox, google+, and facebook all allow for automatic uploading saving you the need to do it later. Want them on your PC also well dropbox has a client for PC syncing so I never need to manually do it! Plus all my photos and videos are now automaticly backed up!
Documents / OneNotes! I'm using skydrive purely because I'm a PC fan boy but drop box could be used also. With one note and skydrive you always have access to your notes on the go or from any PC!
Books again store your libary in the cloud and just download / sync the ones you need now or the ones you know you will need when your offline.
Navigation! After being forced to use Windows phone and Nokia Drive you really appreciate Google navigation. Ok no offline navigation but still...